Dimensions.—Shell 0.07 long, 0.11 broad.
Habitat.—South Pacific, Station 297, depth 1775 fathoms.
17. Dictyospyris polystoma, n. sp.
Shell nut-shaped, mammillate, with distinct sagittal stricture. Pores small and numerous, irregular, on each side of the ring three to five times as large as on the lateral sides. Basal plate with twelve large pores (four central and four alternate pairs of peripheral).
Dimensions.—Shell 0.1 long, 0.14 broad.
Habitat.—Tropical Atlantic, Station 338, depth 1990 fathoms.
Family LIII. Tholospyrida, n. fam.
(Pl. [87], figs. 7-10; Pl. [89], figs. 1-4; Pl. [95], figs. 14-16).
Definition.—Spyroidea with a galea, but without thorax; the shell being composed of the bilocular cephalis and of an aboral cupola or galea arising from its coryphal face.
The family Tholospyrida differs from the preceding Zygospyrida, its ancestral group, in the development of a galea, i.e., a fenestrated hemispherical or dome-shaped cupola, which covers the upper face of the cephalis like a cap.